Charge forming device



Jan. 24, 1950 H, TA 2,495,299

CHARGE FORMING DEVICE Filed Sept. 50, 1947 INVENTOR.

HA /WP) 6. 753727? Patented Jan. 24, 1950 2,495,299 CHARGE FORMINGDEVICE Henry G. Tarter, South Bend, Ind, assignor to Bendix AviationCorporation, South Bend, Ind a corporation of Delaware ApplicationSeptember 30, 1947, Serial No. 777,063

4 Claims. (Cl. 128-119) This invention relates to charge forming devicesor carburetors for engines, and particularly to so-called injectioncarburetors commonly used on aircraft engines, and an object of the sameis to provide in such devices means whereby when a cold engine is to bestarted and warmed-up under low temperature conditions preparatory toplacing it under load, an enriched fuel mixture may be selectively orautomatically supplied to the engine until such time as the latter isable to operate efficiently on normal fuel mixtures;

In the type of injection carburetor and direct injection systems withwhich the present invention is concerned, fuel mixtures in the idlerange and up to low cruise are controlled by a contoured idle valvewhose position is varied in relation to throttle opening. This givessatisfactory operation over a wide range of temperatures, but where thesurrounding temperature is relatively low, it may prove desirable toenrich the idle and warm-up fuel mixtures; and the present inventionprovides'improved means for accomplishing this result.

The foregoing and other objects and advantages will become apparent inview of the following description taken in conjunction with thedrawings, wherein:

The sole figure is a sectional schematic of an injection carburetorhaving an idle enrichment control constructed in accordance with theinvention.

Referring to the drawing, a main air intake conduit It) leads to asupercharger ll of an internal combustion engine generally indicated atI2. The conduit I is controlled by a throttle l3 operable from thepilots cockpit in a known manner, and anterior the throttle is a largeventuri l4 and a small venturi 15. In the type of fuel supply systemused to illustrate the present invention, the pilot controls the airsupply by manipulating the throttle l3 while the liquid fuel is sprayedunder pressure into the air conduit posterior the throttle by means of anozzle IE, to which the fuel is metered under pressure automatically bythe apparatus hereinafter described more or less in detail. It will lbeunderstood, however, that the nozzle it, instead of discharging into themain air intake conduit, could discharge directly into an enginecylinder and could comprise one of a series of nozzles of a directinjection system as in the copending application of LeRoy J. Evans,Serial No. 475,783, filed February 13, 1943, now Patent No. 2,447,268,issued August 19, 1948.

The fuel metering apparatus is mounted in a casing or housing generallyindicated at 20; it may be considered as made up of two main sections,viz., a regulator unit l8 and a control unit IS. The regulator unitcomprises a poppet valve 2| arranged to slide in a valve body 22 formedwith an annular chamber 23 and a series of inlet ports 23 to which fuelis supplied under substam tially constant pressure by way of conduit 24.Such pressure may be maintained by a conventional fuel pump, not shown,having a by-pass controlled by a valve set to open at a predeterminedpressure, for example, sixteen to eighteen p. s. i. An air'diaphragm 25and a fuel diaphragm 26 have their outer edges secured between adjacenthousing sections and their central portions clamped between a series ofbushings secured on the stem 21- of the poppet valve 2|. Thesediaphragms, together with a rigid partition 28 and a sealing diaphragm29, divide the housing 20 at this point into a series of chambers, viz.,air differential chambers A and B and fuel differential chambers C andD. Chamber A is subjected to a measure of air intake pressure by meansof a series of impact tubes 30, which have their entrance or intake endslocated adjacent the carburetor deck and communicate with chamber A byway of annular chamber 3 I, valve port 32 and passage 33. Chamber B issubjected to Venturi suction by means of annular channel or chamber 34formed in the throat of the small venturi I5 which communicates withsaid chamber by way of passages 35 and 35. Chambers C and D. aresubjected, respectively, to metered and unmetered fuel pressures. Thesmall diaphragms 36 and 31 serve the purpose of balancing regulatorsystem including the poppet valve 2|; they are connected to oppositeends of the valve and form movable walls of chambers 38 and 39 to whichunmetered fuel pressure is communicated from chamber D by small passages40 and 4|. The diaphragm 31 also has a sealing function. The airchambers A and B are interconnected across the diaphragm 25 by a smallpassage 42 having a bleed 43 therein, and port 32 in air passage 33 iscontrolled by a capsule or aneroid shown asa sealed corrugated bellows44 which is mounted in a housing 45 open to the air intake conduit l0and carries a valve member or needle 46 adapted to vary the area of saidport. The bellows 44 is loaded in a manner such as to render itresponsive to changes in both pressure and temperature (see Patent No.2,376,711 to Frank C. Mock), and is therefore responsive to changes indensity. Thus, at relatively high barometric pressures, as for example,

no metering effect.

those usually prevailing at or near sea level, the bellows tends tocollapse and open port 82 and passage 33, while at relatively lowbarometric pressures, as for example those usually prevailing at highaltitudes. the bellows tends to expand and close port 31 and restrictflow of air through passage 33. As passage 33 becomes more and morerestricted, the differential across air diaphragm 25 is reduced, tendingto reduce travel of the poppet valve 2| for a given change in throttleposition and conseqently the fuel-air ratio, as will be more fullyexplained in the description of the operation of the invention.

richment fuel during the early part of the power enrichment range, theJet [53 taking overat higher power flows. The metering jets are locatedin flow channels which open into a fuel discharge conduit 53 throughports controlled by a manual mixture control valve 51 secured on arotatable shaft 58 provided with a lever or handle as. Metered fuelpressure is communicated back to chamber C of the regulator unit it byway of a duct or conduit 60. VA regulator fill valve 8i, operated by acam on the shaft 58, permits chamber C to fill with fuel through duct orconduit Gil when the carburetor is to be placed in operation after ithas emptied, said valve 6! being held open in all positions of themixture .control valve 57 except idle cut-off. For a more detaildescription of the fill valve, see Patent No. 2,361,227 to F.- C. Mock.Conduit 58 conducts metered fuel under pressure to the discharge nozzleit, which may be set to open at a predetermined pressure, for example,ten p. s. i. A passage or duct 62 vents chamber C to discharge conduit56 to insure removal of any accumulation of air or vapor in saidchamber.

An idle spring is indicated at 65. Its purpose is to provide an enrichedfuel-air ratio for idling speeds. A screw 66 is readily accessible foradjustment by removing cap 61, the said spring preferably being set soas to act on the poppet valve 2| and urge it toward open position onlywhen the said valve is nearly closed.

In the passage 50 which conducts unmetered fuel to the jets is an idlevalve port 68 which is controlled by idle valve 53, the latter beingconnected to the throttle linkage in a manner such that when thethrottle is closed or nearly so, the idle valve comes into play andcontrols or meters the idle flow permitted by the action of spring 65 tothe desired value. Part of the linkage which connects the idle valve tothe throttle is indicated at 10. As the throttle opens more and more,the idle valve opens and increases the idle flow, until when the lowcruise range is reached, the valve attains its fully open position andhas Any preferred type of idle system may be adopted, that shown beingfor the purposes of illustration only. For other types see for examplethe copending applications of Frank C. Mock, Serial No. 538,153, filedMay 31, 1944, and Arthur J. Volz et al., Serial No. 696,690, filedSeptember 13, 1946.

While the idle system may provide a sufliciently rich starting andwarm-up mixture for average temperatures, yet when operating in coldweather or unusually cold climates, it may prove desirable to furtherenrich the fuel-air ratio to facilitate warming-up of the enginepreparatory to placing it under load. and also for starting the engine,if desired. Withthis in view, a bypass channel or conduit II has itsinlet end disposed to receive fuel upstream of the idle valve 89 and itsdischarge end located downstream of said valve, a restriction 12 beingremovably inserted in said by-pass. A valve 13 controls flow throughconduit H, and this valve is preferably operated automatically inresponse to an engine condition. Accordingly, said valve is shown asmally urged toward closed position by a spring ii. A solenoid coil 15 issupported in the housing H, and this coil is energized when an electriccircuit, comprised of wires H and 78 and a battery 19 or other suitablesource of potential, is closed by a switch 80. As shown, the switch 80is of the thermal type, it being connected by a rod 8| to a piston 82,the latter being slidingly mounted in a cylinder loaded with atemperature responsive material or fluid in heat exchange relation to athermal element 83 located at a point with respect to the engine whereit will respond to engine operating temperature, as for example,cylinder head temperature, oil temperature, or any other pointindicative of engine temperature. A spring 84 normally urges the switch80 to closed position. The electric circuit is preferably connected upwith a master or main ignition switch 85 so that the circuit will bebroken when the ignition is turned off.

Operation When the engine is running, air is drawn into the air intakeconduit ill and through the boost venturi l5 and main venturi M, and adifferential pressure is created between the throat of the small venturiand. the air inlet which at constant entering air density isproportional to the square of the quantity or air flowing. Theserespective pressures are transmitted to chambers A and B of the fuelregulator unit on opposite sides of the air diaphragm 25 and create anet force on the diaphragm tending to open the fuel valve 2|, this forceusually being termed the air metering force. If this force wereunopposed, the fuel valve 2| would tend to move to full open position;but when the valve opens, fuel under pressure flows into unmetered fuelchamber D and through conduit 50 to the fuel control unit,

where it flows through any one or more of the respective meteringorifices, depending upon the position of the manual control valve 51,and thence to the discharge conduit 56 and discharge nozzle it, fromwhich it is discharged under pressure to the air stream flowing to theengine. Chamber D is subjected to unmetered fuel pressure and chamber 0to metered fuel pressure, and the differential between these respectivepressures acts upon the diaphragm 26, tending to move the fuel valve 2|to the left, or in a direction to close the valve. This force iscommonly termed the "fuel metering force" and it opposes the airmetering force. The valve 2| is thus caused to adjust itself to a pointof equilibrium such that the differential pressure across the fuel 5.manner substantially constant fuel-air proportioning is maintained. Asengine speed is decreased, the rate of air flow to the venturi isdecreased, thereby decreasing the differential pressure acting on thediaphragm 25, causing the valve 42 to move towards closed position andthus decrease the fuel flow to compensate for decreased air flow. Thus,the air metering force controls the fuel metering force. Since theVenturi-toair scoop differential pressure increases upon a decrease inentering air density, the differential pressure across the diaphragm 25will tend to a increase, thereby increasing the fuel flow and enrichingthe mixture. The automatic control unit including the bellows 44 coactswith the calibrated bleed 43 in channel 42 to prevent such enrichment,said bleed bein substantially ineffective to vary the differentialpressure in these chambers and across the air diaphragm 25 at such timeswhen the needle valve 46 is in open position, as at ground level, bybecoming increasingly effective in reducing the differential pressurewhen said needle progressively restricts the port 32 and consequentlythe passage 33 with increase in altitude. Thus,,for any given mass airflow, the needle 46 will so restrict the passage 33 with variations inaltitude that the differential pressures in chambers A and B will remainconstant notwithstanding that the differential in pressure at venturi land the impact tube 30 increases with a decrease in entering airdensity.

At low air flows, the differential across the air diaphragm may bereduced to a point where the poppet valve will not open sumciently toprovide adequate head for idling purposes, and it is therefore desirableto provide some means of holding the valve open at idling andnear-idling speeds of the engine. It is for this reason that the idlespring 65 (or some other idling arrangement such as those disclosed inthe copending Mock and Smith applications) is provided, the said spring65 being adjusted in a manner such that it holds the fuel valve openwhen the air differential drops to a predetermined value. This willinsure an ample fuel metering head for the idle valve 69, which comesinto play at low air flows and meters the idle fuel.

Under low temperature conditions, however, it may become desirable toprovide an added enrichment for idlin and near-idling speeds; and

it is under these conditions that the valve 13 comes into operation toopen the passage 1| and permit fuel to by-pass the idle valve and enrichthe idling or near-idling mixture. In the form of the inventionillustrated,'the valve 13 is operated automatically, the circuit TI, 18being rendered operative when the master switch 85 is turned on orclosed; and assuming at this time that the temperature of the engine issuch as to cause the thermal switch 80 to close, then the I solenoid 16will be energized and the valve 13 will be opened and fuel will not onlyflow through the idle valve port 68 (assuming an idle setting of thethrottle), but will also flour through the channel ll to the dischargenozzle 16. As soon as the engine attainsv a predetermine operatingqtemperature, the thermal element 3 expan s and opens the switch SIM thelatter remaining open'untilthe temperature again dro s to a'relativelylow value. If desired, an additional manual switch may be introducedinto the circuit, so that valve 13 may be operated automatically only atsuch times as conditions warrant. For selective manual operation, thesolenoid valve I3 could be operated by the pilot, in which event thethermal switch -83 could be dispensed with. Another example would be tosubstitute a mechanical valve for the solenoid valve 13 and operate themechanical valve by a. hydraulic circuit with a thermal indicator actingto open and close the valve.

Although only one embodiment of the invention has been illustrated anddescribed, it will be obvious that others will be obvious in view of theteaching of the invention, and that various changes in the form andrelative arrangement of the parts may be made to suit requirements.

I claim:

1. In a, fuel supply system for an engine, a flow channel provided witha metering restriction, a fuel valve for regulating the metering headadapted to respond to differential pressures constitutin a function ofthe flow of air and fuel to the engine, an idle orifice in series flowrelationship with said restriction, an idle valve for controlling saidorifice and arranged to meter idle fuel at low air flows, a conduitby-passing said orifice and valve, a valve controlling said conduit, andmeans for operating said latter valve.

2. A fuel supply system as claimed in claim 1 wherein said valveoperating means includes a thermal device responsive to changes inengine operating temperature.

3. In a fuel supply system for an engine having a throttle controlledair intake, a flow channel provided with a metering restriction, a fuelvalve for regulating the metering head across said restriction,diaphragm means connected to said valve and arranged to respond todifferential air and fuel pressures constituting a measure of the flowof air and fuel to the engine, means for maintaining a minimum head offuel irrespective of low air flows, an idle valve movable in relation tothrottle position for metering the fuel at idle and near idle speeds ofthe engine, a fuel conduit by-passing said idle valve and having ameterin restriction therein, a valve controlling said latter conduit,and means for operating said latter valve to enrich the idle fuel.

4. A fuel supply system as claimed in claim 3 wherein the valvecontrolling said by-pass conduit is of the electric type and the meansfor operating the valve comprises an electric circuit having a thermalswitch therein including a thermal element responsive to changes in theoperating temperatures of the engine.

HENRY G. TARTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

